There is known a conventional method of measuring a distribution of strain or temperature in the longitudinal direction of an optical fiber by means of Rayleigh backscattering light (hereinafter, abbreviated as Rayleigh scattering light) of tunable laser light pulses launched into the optical fiber and using relationships between the variation amounts of strain, temperature, the scattering light from the optical fiber and a correlation peak frequency of the scattering light received from each longitudinal position of the optical fiber (see, for example, Patent Document 1).
Further, there is another technique in which both reference data and target data from a measurement target are measured and a correlation analysis for calculating in the frequency domain a correlation between these data is performed, to obtained a Rayleigh spectrum shift (see, for example, Patent Document 2).
Furthermore, there is also a hybrid measurement technique for sophisticating the measurement utilizing Rayleigh scattering, in which a position or a distance to the position of measurement data obtained by Rayleigh scattering is corrected using combination of measurement data obtained from Brillouin scattering in addition to the Rayleigh scattering (see, for example, Non-Patent Document 1).